Method and apparatus for casting



May 31, 1938. J. FLAMMANG ET AL y y METHOD AND APPARATUS FOR CASTINGOriginal Filed Aug. 12, 1931 2 Sheets-Sheet l imwbowi May 31, 1938. J.FLAMMANG ET AL METHOD AND APPARATUS FOR CASTING 2 Sheets-Sheet 2Original Filed Aug. 12, 1931 a a 1 G A 7 H Hun a w x Patented May 31,1938 UNITED STATES PATENT OFFICE Bowser and Herman Ernst, St. Louis Mo.,as-

signors to The Sterling Corporation, St. Louis, Mo., a corporation ofDelaware Application August 12, 1931, Serial No. 556,568

, Renewed July 8, 1936 8 Claims.

This invention pertains to a method and means for casting which isparticularly adaptable to the casting of trunk pistons such as are usedin automobile and aircraft engines. Such pistons are often cast of lightmetals, such as aluminum or its alloys and the casting is done inpermanent metal molds.

A number of different methods of casting articles of this kind have beenused heretofore 10 with varying degrees of success. Most of thesemethods have disadvantages of one form or another; In practically allprevious methods the metal is delivered to the mold cavity or matrixthru a gate which is relatively narrow compared with the bulk of thecasting. It has been desirable to make the gate narrow in order toreduce the amount of metal contained therein and also in order to leavea relatively small section of metal which must be cut in order to removethe g gate from the casting.

One serious drawback with the above method of casting is that the gateoften sets'or solidifies before the interior metal of the casting hasset. When this happens the flow of molten metal to 25 the casting mustnecessarily cease before the interior metal of the casting has becomesolid. Consequently the interior metal of this part of the castingsolidifies after the exterior portion or outer skin has set. Slnce thesetting or solidify- 30 ing takes place as a result of the cooling ofthe metal, there is still a contraction of the metal going on while theinterior portions are still fluid. Those parts of the casting which haveset continue to contract on account of their cool- 35 ing. The interiorportion which is still liquid is also contracting at this time.Accordingly, the fluid metal which originally had suflicient volume tofill the entire interior portion of the casting will shrink so that itsvolume will be less than 40 it was originally. As a consequence some ofthis metal is withdrawn during cooling from the space it originallyoccupied so that as a result of this action empty spaces or blow-holesare left in the interior of the castings These blow-holes are 45 flawswhich weaken the casting. and are otherwise objectionable.

Another drawback with former casting methods results from the fact thatair is entrapped in the stream of molten metal as it passes into the 50mold cavity. This is due in some cases to the high velocity at which themetal enters where the casting is carried out under a high pressure. Theagitation of the metal entering at a high velocity entraps air with themetal. In other cases where 55 the metal is poured into the mold cavityfrom the top and flows in by gravity, air is entrapped during thepouring and is carried into the mold cavity where the coollng'of themetal entraps air bubbles which remain in the casting.

It is an object of this invention, therefore, to 5 overcome some of theabove mentioned objections to the prior casting methods.

Another object is to provide a method in which the entrapping of airwith the inflowing metal is avoided. l0

Another object is to provide a method in which the air in the moldcavity is permitted to escape therefrom before the cavity is entirelyfilled with molten metal.

Another object is to provide a method and 15 means whereby the supply ofmolten metal to the interior parts of a casting may be continued untilthose interior parts have set so as to avoid the formation of blow-holesand crystallization shrinkage by the contraction of the metal.

Further objects will appear from the following description taken inconnection with the accompanying drawings, in which:

Figure 1 is a side view partially in section of a casting apparatusembodying this invention and adapted for carrying out the methodthereof;

Figure 2 is a cross sectional view of a piston casting shown in itsrelation to the casting nozzle and representing the casting just afterthe metal of the casting itself has completely set. This figure is asection on line 2--2 of Fig. 3;

Figure 3 is a section on line 3-3 of Fig. 2.

In accordance with the method of this invention the metal is caused toflow into the mold cavity upwardly from the bottom. The mold cavity isvented in any suitable manner. In many types of castings the mold mustbe constructed so that it may be opened to free the casting. In

such cases the cracks between the adjoining faces of the mold sectionsusually provide suflicient 40 venting space for the escape of air fromthe mold cavity. The metal is flowed into the mold cavity under amoderate pressure so that it enters at a moderate velocity. The pressureis so adjusted that the metal will flow into the mold quietly withoutundue agitation so as to avoid entrapping air in the flowing metal. Atthe same time the mold cavity is filled slowly enough so that the airtherein may escape thru the vent openings in advance of the flowingmetal. Since the metal enters at the bottom and the air escapes at thetop all danger of entrapping air is eliminated.

A particular feature of this invention is that arrangements are suchthat the flow. of molten metal into the mold is so regulated that thenatural cooling of the casting metal in the mold causes the casting toset first in that portion which is most distant from the gate, and thesetting 01 the metal progresses gradually toward the gate. As aconsequence of this action those parts of the casting which are stillfluid at any time are still in communication with the source of moltenmetal. Accordingly, the flow of molten metal is maintained to suchportions 01' the casting as are still fluid.

In order to accomplish this result the manner and rate of cooling ofdifferent parts of the casting should be taken into account. Where thecasting has certain portions which are more massive than other portionsso that more metal is required to fill that part of the mold, suchmassive portions must be filled quickly so that ample time is allowedfor cooling and setting before lighter portions nearer the gate becomesolid and cut ofl the supply of molten metal to such massive parts. Adirect flow of metal to such massive portions is, therefore, desirable.In accordance with this invention the gate is so formed as to provide adirect path for the molten metal to such massive parts as the wrist pinbearings so that a rapid delivery of metal to those parts may beaccomplished. This arrangement also provides a direct path for the flowof heat from the incoming molten metal to those parts in the path ofsuch flow so that they are maintained fluid until the more distantportions have a chance to set.

In a trunk piston the head portion in which the packing ring grooves aresubsequently formed is usually somewhat thicker and contains more metalthan the skirt portions. In some types of pistons the head is also madeheavy. Since these portions are somewhat massive and the cooling thereoftakes place progressively from the outside toward the interior it isimportant to maintain a flow of molten metal and also a flow of heat tothe interior portions of these massive parts until setting is complete.In other words the piston head should be the last part to become solidsince the delivery of metal to the other parts in the method of thisinvention takes place thru the head.

In accordance with this invention, therefore, the gate in the mold is soformed as to facilitate maintaining the head portion of the casting influid condition until the remaining portions have set. This isaccomplished by providing a gate having a contracted portion at a pointtherein spaced from the piston head. The gate is relatively shortbetween the source of molten metal and the casting. Accordingly, theheat of the molten metal supply keeps the metal in the gate molten andalso extends its influence to the adjacent portion of the piston head soas to maintain that portion fluid as long as possible. This contractedportion of the gate may be said to act as a sort of heat valvecontrolling the rate of flow of heat to the piston head. By adjustingthe spacing of this contracted point from the piston head the rate ofheat flow to the casting from the source of molten metal can be adjustedrelatively to the rate of heat flow away from the casting thru the mold.Such adjustment is made so that the setting of the metal takes placeprogressively from the distant portions of the casting toward the gateand particularly from the outer circumference of the piston head towardits center where the gate enters the casting. When this adjustment isobtained the central portion of the piston head is the last to set. Itmay in fact be maintained fluid for a short time after its naturaltendency to set by the flow of heat thereto thru the gate from thesource of metal. During this final solidification, the contraction ofthe metal in that portion is supplied by a fiow of molten metal from theretort up to the final moment of setting. When the casting hascompletely set, the mold may be separated from the source of metal.

Referring to the drawings, l designates a furnace of any suitable typecontaining a retort 2, in which the casting metal is melted, andprovided with any suitable means 3 for heating the retort. A nozzle orspigot 4 dips into the molten metal in the retort. The retort isequipped so that it may be closed air-tight and an air connection 5 isprovided by means of which pressure may be applied to the interior ofthe retort in order to eject the molten metal.

A mold 6 which may be of any suitable type is mounted on a frame Ihinged at 8 on the furnace structure so that it may be lowered upon theretort or raised thereabove. The mold 6 may be of any suitable typeaccording to the shape of piston to be cast and is preferably suitablyvented. In the illustration of the drawings a piston mold is shownhaving a removable core 9. This core may be of the collapsible type orof any other construction suitable for the purpose. In the apparatusillustrated in the drawings a hydraulic cyl- .3

inder I0 is arranged for withdrawing the core 9 and other suitablehydraulic or air-controlled devices I I may be arranged in any desiredmanner to open the mold 6. These devices for operating the mold form nopart of the present invention. A description of suitable piston moldingapparatus applicable to the present invention may be found in Patent No.1,952,201 issued March 27, 1934. The weight of the mold and itsconnected parts may be counterbalanced by a weight l2 hung on a cablel3, passing over a pulley l4 on an upright support l5 and connected tothe frame I in any suitable manner.

The top of the nozzle 4 has a face, the outer portion of which is planeto match the face of the bottom of the mold 6 with which it engages. Thecentral portion of the nozzle 4 may be provided with an upstanding tip30 arranged to project into the gate of the mold so as to assist intransferring heat to the metal therein. An insulating plate or washer 3|of asbestos or other suitable material may be interposed between thenozzle 4 and the mold 6 so as to avoid unduly heating the mold, and toprevent leakage of metal.

In the operation of casting the empty mold with its core in place ispressed down upon the nozzle 4 by swinging the frame I downwardly uponits hinge. The air pressure is then applied to the connection 5 so as toapply pressure to the surface of the liquid metal in the retort 2, thusforcing the metal out of the nozzle 4 and into the mold 6. A moderatepressure is applied for this purpose sumcient to lift the metal to thetop of a mold cavity so as to completely fill the same. The pressure isnot so great as to cause the metal to flow into the mold at a highvelocity. Accordingly, the metal rises in the mold cavity at arelatively slow rate so as to permit the air in the mold to escape bythe vent openings. The velocity of inflow is, however, suflicient toinsure that the mold cavity is completely filled before the metal sets.It will be noted that this procedure differs from so-called pressurecasting, in which the metal is forced into the mold under a highpressure, in that the moderate pressure here employed need not greatlyexceed that required to lift the metal into the mold. The gentle flowobtained is, therefore similar to the flow obtained in gravity pouring,but in the present method the metal enters the mold at the bottominstead of at the top.

In such castings which have portions heavier (i. e., portions of greatervolume) than other portions thereof, the mold bavity is preferably soarranged that these heavier portions will be lowermost and that the gatecommunicates as directly as possible with these heavier portions. In theillustrations of Figures 2 and 3 the piston casting has its heavierportion, representing that portion in which the packing ring grooves arecut and the head portion l1, placed at the bottom. In the pistonillustrated, there is also a fairly heavy rib l8 extending across thehead.

' In such castings when made by previous methods, it has been founddiflicult to avoid blowholes or porosity due to crystallizationshrinkage in the portions l6, I1, and i8. As is well understood theavoidance of such defects is particularly important in this type ofpiston and especially in the head portions thereof.

In accordance with this invention the gate I9 is placed so as to enterthe head portion II of the casting at substantially the middle thereof.The gate I9 is provided with a contracted neck 20 spaced at appropriatedistance from the head l1. Extending in opposite directions from thegate l9 and along the direction of the wrist pin axis are lateral wingportions 2i which may be tapered toward the outer circumference of thepiston head. \These wing portions may be relatively narrow and provide adirect path for the flow of metal to those sides of the piston where thewrist pin bearings are located. Accordingly, a rapid flow of metal tothese portions is possible and a direct path for fiow to massiveportions of the casting is provided. This prevents the metal fromsetting before it arrives at its proper place in the mold, and maintainsthe same in a sufficiently fluid condition to work into all parts of themold cavity so that a perfect casting may be formed. Also these wingportions very materially assist in taking care of crystallizationshrinkage in portions l6, l1 and i8 by feeding metal directly to theseportions.

The contracted neck 20 provides a point in the path of flow where thatpath is most restricted. This point is spaced appropriately both fromthe body of the casting and from the spigot 4. It will be noted that theflow of molten metal to the casting is most rapid at this point. Thereis also a flow of heat through the metal from the heated spigot to thecasting and this fiow of heat is also most concentrated at the neck 20.Accordingly the best conditions for fluidity of the metal flowing to thecasting are found at the neck 20. It will be seen that the entireorganization is such that the metal flows to the mold cavity in such amanner as to rise in said cavity in a symmetrical manner. Once thecavity is filled with metal, solidification begins. The parts whichfirst solidify are necessarily those most distant from the spigot, thatis the upper rim of the skirt. As the heat flows away from the castingat all points within the mold but additional heat flows to the castingfrom the spigot through the gate, it will be clear that thesolidification takes place progressively from the top downward along thepiston. Under these conditions the last portion to solidify is thepiston head and as the flow of heat from the spigot continues thecentral portion of the head which is next to this source of heat willremain liquid longest. During this solidification there is always moltenmetal capable of flowing situated between the solid parts and the sourceof new metal. Accordingly any contraction involved in the solidificationis supplied by new metal from the source so that faults due tocrystallization shrinkage are entirely avoided. The solidification ofthe casting, therefore, continues progressively until finally the gateportion becomes solid. As the neck portion 20 has the greatestconcentration of heat it will still be liquid when the rest of the gatesolidifies. Accordingly when the mold is removed from the spigot thisliquid portion returns to the spigot and the gate is terminatedpractically at the neck 20.

In order to insure free flowing of the metal and that it will remain ina sufllciently fluid condition until it arrives even at distant parts ofthe mold cavity the nozzle 4 may be separately heated by any suitablemeans, such as jet 22 arranged to project a flameagainst the nozzle. Inaccordance with this invention the nozzle is heated to such atemperature as to maintain the liquid metal therein at a temperaturesubstantially above the normal melting point of the metal. For instance,if the normal melting point of the casting metal is 1100 F. the nozzlemight be maintained at such a temperature as to keep the metal thereinat about 1300 F. It has been found that by thus heating the molten metaljust as it enters the mold it is maintained in a highly fluid conditionuntil it has had a chance to enter all crevices of the mold cavity so asto form a perfect casting, after which it cools gradually, setting firstat the extreme ends furthest from the gate and progressively thereafteralong the piston, the head portions setting last. The insulating pad 3|insures that the high temperature of the nozzle 4 shall. not unduly heatthe mold itself. Accordingly the absorption of heat from the casting bythe mold is not interfered with.

At the same-time the tip 3|] of the nozzle extending into the gate isadapted to deliver heat to the metal therein from the highly heatednozzle, and thereby prevent premature setting of the lower portion ofthe casting. By maintaining the molten metal as it passes to the castingat a superheat temperature, as specified above, and maintainingcontinual communication between the main body of metal and that whichhas already entered the mold, it will be noted that a definitetemperature gradient is established from the point of superheat to themetal in the mold. By maintaining a superheat temperature, a gradient ofconsiderable slope is established and, accordingly, there will be a flowof heat along the flowing column of metal to the metal in the.mold. Sucha flow of heat does more than compensate for loss of heat by the metalen route to the mold. It supplies an extra quantity of heat to the metalalready in the mold. As a'consequence the metal may be flowed into themold at a low rate in a gentle manner and will retain suflicientfluidityto enter all of the minute interstices of the mold without the necessityof applying a high pressure thereto. By thus flowing the metal in aquiet and gentle manner into the mold, excessive agitation is avoidedand the chances of entrapping air in the flowing metal are reduced to aminimum. By heating the spigot to a temperature substantially above thefreezing point of the metal, the temperature gradient, which would beinsignificant under the conditions of ordinary practice, is stepped upat the point where the metal passes the spigot and, accordingly, a morerapid flow of heat to the metal in the mold is promoted. By this method,therefore, the metal may be maintained in a fluid condition until itreaches the farthest points of the mold cavity and thereafter thecooling of the casting takes place in a symmetrical manner from thefarthest points toward the gate. As the heat flow along the incomingmetal is maintained, the portion near the gate is the last to becomesolid and, as it is in continual communication with fresh metal,shrinkage is compensated for continually as it takes place by a flow ofnew metal to the casting.

It will be seen, therefore, that this invention provides a simple andeifective method and apparatus by which castings may be formed free ofblow-holes, crystallization shrinkage and other contraction flaws. Themethod is easily carried out and is inexpensive to apply to practicallyany type of piston casting.

While a certain theory of action has been used in describing thismethod, such theory is advanced only for the purpose of explanation. Itis understood, therefore, that the invention is not limited to anyparticular theory of operation. It is also understood that while bothmethod and {apparatus have been described as a. unitary whole,

#bertain individual features or sub-combinations thereof, may be usefuland the employment of such individual features and sub-combinations iscontemplated by this invention and is within the scope of the appendedclaims.

As stated previously, this invention is applicable to the casting oflight metals of which aluminum and its alloys are examples, otherexamples being magnesium and its alloys. It is, therefore. to beunderstood that the word aluminum, appearing in the claims, is useddescriptively and not limitatively.

It is further obvious that various changes may be made, within the scopeof the appended claims, in the details of construction and operationwithout departing from the spirit of this invention; it is to beunderstood, therefore, that this invention is not limited to thespecific details shown and/or described.

Having thus described the invention what is claimed is:

1. Apparatus for casting trunk pistons provided with wrist-pin bearings,comprising, a mold having a piston-forming matrix arranged with thepiston head lowermost, and having a gate entering the matrix at themiddle of the piston head and provided with lateral wing pora tionsextending in opposite directions across the piston head along the wristpin axis.

2. Apparatus for casting trunk pistons, comprising, a mold having apiston-forming matrix arranged with the piston head lowermost, andhating a gate entering the matrix at the piston head, and means forheating the metal flowing through said gate substantially above themelting point of the metal, said means extending into said gate.

3. Apparatus for casting trunk pistons, comprising, a mold having apistonrming matrix arranged with the piston head lowermost, and

having a gate entering the matrix at the piston head, a spigot for themolten metal leading to said gate, and means for heating said spigotsubstantially above the melting point of the metal, saitd spigot havinga part extending into said ga e.

4. Apparatus for casting trunk pistons, comprising, a mold having apiston-forming matrix arranged with the piston head lowermost, andhaving a gate entering the matrix at the piston head, a spigot for themolten metal leading to said gate, means for heating said spigotsubstantially above the melting point of the metal, and heat insulationbetween said spigot and said mo d.

5. Apparatus for casting trunk pistons, comprising, a mold having apiston-forming matrix arranged with the piston head lowermost, andhaving a gate entering the matrix at the piston head, a spigot for themolten metal leading to said gate, means for heating said spigotsubstantially above the melting point of the metal, and heat insulationbetween said spigot and said 'mold, said spigot having a part extendinginto said gate.

6. The process of casting trunk pistons in permanent molds, comprising,with the piston head lowermost, flowing the molten metal from a sourceupwardly into the mold in a path symmetrical with refercnce to thepiston axis, and n heating the inflowing metal substantially above itsfusion temperature so as to produce an inflow of heat to the metal inthe mold along with the inflowing metal such as to cause solidificationthereof progressively downwardly and symmetrically with respect to saidaxis.

7. In the art of casting aluminum, the process comprising, maintaining alarge body of molten metal at a temperature sufiiciently above thefreezing point thereof to render the metal fluid, lifting the moltenmetal in a gentle flow upwardly from said body into a mold, and addingheat to the flowing metal after it leaves said body and before it entersthe mold so as to maintain a suiiicient temperature gradient from thepoint of heat application in the flowing metal stream to the remotestmolten metal in the mold to cause a progressive setting of the castingfrom the remotest part toward said point.

8. In the art of casting aluminum, the process comprising, maintaining alarge body of molten metal at a temperature sufilciently above thefreezing point thereof to render the metal fluid, lifting the moltenmetal in a gentle flow upwardly from said body into a mold, applying tosaid body of metal a moderate pressure limited so as not greatly toexceed that required to lift the metal into the mold and maintainingsuch pressure so limited until the casting sets, and adding heat to theflowing metal after it leaves said body and before it enters the mold soas to maintain a sufllcient temperature gradient from the point of heatapplication in the flowing metal stream to the remotest molten metal inthe mold to cause a progressive setting of the casting from the remotestpart toward said point.

JOHN FLALJIVIANG. PERCY L. BOWSER. HERMAN ERNST.

